N,n-di(2-benzothiazolyl)sulfenamides useful as vulcanization activators

ABSTRACT

COMPOUNDS OF THE FORMULA   ((X-BENZOTHIAZOL-2-YL)2-N-S-)N-R   WHEREIN X IS HYDROGEN, ALKYL, ALKOXY, NITRO, HALO, OR HYDROXY AND N IS ONE OR TWO; WHEN N IS ONE R IS ALKYL, CYCLOALKYL, ARALKYL OR ARYL; WHEN N IS TWO R IS ALKYLENE WHICH COMPOUNDS ARE DELAYED ACTION CURE ACTIVATORS FOR RUBBER.

United States Patent US. Cl. 260-305 6 Claims ABSTRACT OF THE DISCLOSURE Compounds of the formula wherein X is hydrogen, alkyl, alkoxy, nitro, halo, or hydroxy and n is one or two; when n is one R is alkyl, cycloalkyl, aralkyl or aryl; when n is two R is alkylene which compounds are delayed action cure activators for rubber.

This is a division of application Ser. No. 110,658 filed Jan. 28, 1971, now US. Pat. 3,689,467 issued Sept. 5, 1972.

BACKGROUND OF THE INVENTION This invention relates to new compounds useful as activators for the vulcanization of rubber.

Activators, sometimes called secondary accelerators, are used by manufacturers of vulcanized products to improve the vulcanization process by reducing the time required to cure a vulcanizable composition. Commonly used activators are diphenylguanidine and thiuram sulfides, however, their use adversely affects the processing safety of the stocks and as a consequence, prevulcanization inhibitors may have to be used to avoid premature vulcanization of certain stocks. The compounds of this invention possess a valuable combination of properties in that they activate the vulcanization cure rate and also inhibit premature vulcanization. These and other advantages of the invention will become apparent as the description of the invention proceeds.

SUMMARY OF THE INVENTION The compounds of this invention are characterized'by the formula wherein X is hydrogen, lower alkyl, lower alkoxy, nitro, chloro, bromo, iodo, or hydroxy and n is one or two; when n is one'R is "alkyl, cycloalkyl, aralkyl or aryl; when n is two R is alkylene. The alkyl radical may be'primary, secondary or tertiary and the alkyl chains thereof may be branched orhribranched. Alkyl radicals of 1-20 carbon atoms are suitable with radicals of 1-10 carbon atoms being preferred. According to this invention lower alkyl means radicals of 1'-5 carbon "atoms. Cyc1oalkyl radicals of 5-12 carbon atoms are suitable with radicals of 5-8 carbon atoms being preferred. Aralkyl is a monovalent alkyl radical having a phenyl radical attached to a carbon atom of the alkyl chain. Aralkyl radicals of 7-10 carbon atoms are preferred. Aryl is a 'monovalent radical derived by removal of one hydrogen atom from an aromatic hydrocarbon. The aryl radical may be substituted in the aromatic nucleus by alkyl groups. Aryl radicals of 6-12 carbon atoms are suitable. Phenyl is the preferred ice aryl radical but radicals of the naphthalene series are suitable. Alkylene means a divalent alkyl radical wherein each valence is attached to an acyclic or cyclic aliphatic carbon atom. Alkylene radicals of 1-8 carbon atoms are preferred. The alkylene chain may be interrupted by a phenylene radical.

Examples of R are methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, amyl, hexyl, octyl, decyl, dodecyl, cetyl, eicosyl, cyclopentyl, cyclohexyl, cyclooctyl, cyclodecyl, cyclododecyl, benzyl, alpha-methyl benzyl alpha,alpha-dimethyl benzyl, phenethyl, xylyl, phenyl, naphthyl, tolyl, 4-ethyl phenyl, ethyltolyl, propylphenyl butylphenyl, hexylphenyl, methylene, dimethylene, trimethylene, l-methyldimethylene, tetramethylene, pentamethylene, hexamethylene, heptamethylene, octamethylene, 1,4-dimethyltetramethy1ene, xylylene and cyclohexylene.

Examples of the compounds of the invention are:

N, N-di 4-methylbenzothiazolyl) cyclohexanesulfenamide,

N,N-di 5 -ethylbenzothiazolyl alpha-toluenesulfenamide,

N,N-di(4-chlorobenzothiazolyl) benzenesulfenamide,

N,N-di (5-bromobenzothiazolyl isopropanesulfenamide,

N,N-di (6-ethoxybenzothiazolyl -n-butanesulfenamide,

N,N-di 6-nitrobenzothiazolyl -2-is0butanesulfenamide,

N,N-di 6-hydroxybenzothiazolyl) cyclohexenesulfenamide,

N,N-di (2-benzothiazolyl methanesulfenamide,

N,N-di 2-benzothiazolyl) ethanesulfenamide,

N,N-di(2-benzothiazoly1)-n-butanesulfenamide,

N,N-di Z-benzothiazolyl octanesulfenamide,

N,N-di(2-beuzothiazoly1) alpha-toluenesulfenamide,

Compounds wherein n isone are prepared by reacting a sulfenyl chloride with'a 2,2'-iminobis(benzothiazole); substituting a bis sulfenyl chloride in the same reaction gives compounds wherein n is two.

The compounds of this invention are excellent delayed action activators for the vulcanization of rubber. The addition of'the'new compounds to sulfur-vulcanizabl"com positions provides stocks-which cure faster'with greater processing safety. Both properties are advantageous to the rubber manufacturer since faster'cure rates decrease the time an "'article'remain's in the vulcanization mold, hence increasing productivity; and greater processing safety eliminates discarding of stocks ruined by premature vulcanization.

The activators of the invention can be used in natural and synthetic rubbers and mixtures thereof. Any diene rubber having sufficient unsaturation to be sulfur vulcanizable is suitable. Examples of suitable synthetic rubbers are styrene-butadiene copolymeri (SBR), isobutyleneisoprene copolymer (butyl), ethylene propylene diene terpolymer (EPDM), butadiene-acrylonitrile copolymer (nitrile), polymers of chloroprene (neoprene) and synthetic polybutadiene, particularly cis-polyisoprene and cis-polyutadiene.

The invention is applicable to vulcanizable compositions containing vulcanization accelerators of various 3 classes and accelerator mixtures. For example, rubber mixes containing the aromatic thiazole accelerators which include N-cyclohexyl-2-benzothiazolesulfenamide, N,N-dialkyl-2-benzothiazolesulfenamide, Z-mercaptobenzothiazole, N-tert butyl-2-benzothiazolesulfenamide, Z-benzothiazolyl diethyldithiocarbamate, 2,2-dithiobisbenzothiazole, 2-(morpholinothio)benzothiazole and 2-(morpholinodithio)benzothiazole may be used. Amine salts of mercaptobcnzothiazole accelerators, for example, the t-butylamine salt, morpholine salt or 2,6-dimethyl morpholine salt of mercaptobenzothiazole may be used in the invention. Any of the thiazole accelarators may be used. The invention is applicable to stocks containing amine antidegradants. Rubber mixes containing antidegradants, for example, N- 1,3 dimethylbutyl-N'-pheny1-p-phenylenediamine, N,N- bis(1,4-dimethylpentyl)-p-phenylenediamine and other phenylenediamines, ketone, ether and hydroxy antidegradants and mixtures thereof, are substantially improved using the process of our invention. Mixtures of antidegradants, for example, a mixture of N-l,3-dimethylbutyl-N-phenyl-p-phenylenediamine and N,N'-bis(1,4dimethylpentyl)-p-phenylenediamine, may be used with the activators of this invention.

For the purposes of this invention, sulfur-vulcanizing agent means elemental sulfur or sulfur-containing vulcanizing agent, for example, an amine disulfide or a polymeric polysulfide. The various types of sulfur-containing vulcanizing agents are known to those skilled in the art of rubber vulcanization.

The amount of activator required in the practice of this invention depends upon other components in the vulcanizable composition. Generally after an amount effective to enhance the vulcanization rate is added, additional amounts do not materially affect the vulcanization parameters. The amount of delayed-action activator added is usually between 0.1 to 2.0 parts by weight, the preferred amount being between 0.2 to 0.5 parts by weight.

DESCRIPTION OF PREFERRED EMBODIMENTS The intermediates of this invention are prepared from Z-aminobenzenethiols as described in Example 1.

Example 1 To a stirred slurry of 43.9g. (0.3 mole) of S,S'-dimethyl cyanoimidodithiocarbonate [Hantzsch and Wolvenkamp, Ann. Chem. 321, 265 (1904)] in 600 ml. of ethyl alcohol, 75.2 g. (0.6 mole) of o-aminobenzenethiol is added in one portion at room temperature. After a few minutes a clear solution is obtained. The mixture is refluxed for five hours during which time a precipitate forms and methyl mercaptan and ammonia are liberated. After cooling to room temperature, the precipitate is recovered by filtration, washed with 100 ml. of heptane and air-dried at 25-30 C. 74 g. (87% yield) of 2,2'-iminobis- (benzothiazole) is obtained which melts at 262-263 C. After recrystallization from dimethylformamide, the. melting point remains unchanged. Analysis gives 14.70% N and 22.28% S compared to 14.83% N and 22.63% S calculated for C I-I N S The product is insoluble in water, ether, acetone, chloroform, benzene, heptane, hexane and ethyl acetate and is soluble in dimethylformamide and dimethylsulfoxide. The pKa value of the product determined in a mixture of water and dimethylsulfoxide is 2.5 X which indicates that the substance is a weak acid.

Substituting 2-amino 5 chloro benzenethiol, 2-amino- 4-chloro benzenethiol, 2-amino-4-nitro benzenethiol, 2- amino 5 hydroxy benzenethiol (4 amino 3 mercapto phenol), 2 amino 4 methyl benzenethiol (2- amino p toluenethiol), 2-amino-4-bromo benzenethiol (Z-mercapto 5 bromo aniline) or 2-amino-5-ethoxy benzenethiol in the above procedure gives the corresponding 2,2'-iminobis(substituted-bcnzothiazole).

Example 2 N,N-di(2-benzothiazolyl)cyclohexyl, phenyl or cyclo- N,N di(2-benzothiazolyl)isopropylsulfenamide.-To a stirred solution containing 0.1 mole of isopropylsulfenyl chloride in ml. of benzene, 0.1 mole of 2,2'-iminobis- (benzothiazole) and 100 m1. of benzene is added in one portion. After stirring at 25-30 C. for 30 minutes, 10.3 g. (0.1 mole) of triethylamine in 50 ml. of benzene is added. The reaction mixture is stirred at 25-30 C. for 16 hours, heated at 56 C. for one hour and filtered hot. The benzene is removed in vacuo. The crude product, M.P. 142- 146 C., is obtained in 67% yield. After recrystallization from isopropyl alcohol, it melts at 148-150 C. Analysis gives 57.36% C, 4.27% H, 11.51% N and 26.66% S compared to 57.10% C, 4.20% H, 11.82% -N and 26.90% S calculated for C H N S The following tables illustrate the improved processing properties obtained by incorporating the new compounds into rubber. For all the rubber stocks tested, as ilustrative of the invention, Mooney scorch times at 121 C. and C. are determined by means of a Mooney plastometer. The time (1 in minutes required for the Mooney reading to rise five points above the minimum viscosity is recorded. Longer times on the Mooney Scorch test are indicative of greater processing safety. The cure characteristics of the stocks are determined by a Mon-v santo oscillating disk rheometer at the indicated temperature. The time (t in minutes required for a rise of two rheometer units above the minimum reading and the time (r required to obtain 90% of the rheometer maximum torque are recorded. The difference (h -j indicative of the cure rate of the stock. Small valiiesof I p-r, indicatefaster cure times. The vulcanizationmate K, is measured in reciprocal minutes. See Coran, 37 Rub ber Chemistry and Technology 689 (1964). Higher values of K indicate higher rates of cross link formation-avulr canizates are prepared by press curing the stocks at .the indicated temperature for the time required to achieve optimum cure as "determined from rheometer data and the physical properties of thevulcanizates are measured and recorded.

The following natural rubber and styrene-butadiene rubber masterbatches are prepared to illustrate the properties of the compounds of this invention. All parts are by weight.

NATURAL RUBBER MAS TERBATCH Smoked sheets 100.0 Zinc oxide 3.0 Stearic acid 2.0 Furnace carbon blac I 45.0 Hydrocarbon softener 5.0

. Total I 155.0

SBR 'MASTERBATCH Oil-extended styrene-butadiene, rubber .1. 137.5 Zinc oxide 3.0 Stearic acid 1.0 Furnace carbon black 65.0 Hydrocarbon softener 1.5

Total I zoaol Vulcanizable compositions are prepared by mixingsul- The data of Table II demonstrate the activity of an fur and accelerator with the masterbatches. To some activator of this invention with diiferentyvulcanization stocks, an antidegradant is also added. The properties of accelerators. The odd number stocks are contnols hav-v the stocks are determined as previously described and are ing accelerator alone whereas the even number stocks shown in Tables II, III and IV. contain the delayed action activator. Note that thestocks 02 57 553 00 7 0 1 .1 %55 2 000 .0 02 05 5 W 0 u 00 6 335 22 m0 mOm mm l fi5 1 22 0m can. m M 1 L 1 1 9 r 13 2 1 n 9 02 n 5 0 411 00000 1 00 .0 6 .2 50 50007 .1 46575 1 2 355 5 "M u m 5% 93 5 6 020 n "6 00m %%%%H m 0 B H 1 n u n 2 0 m 9E 335 m 1 n a 8 02 "5 51 052 0 7 0 00 .06 A 50 5 008 0 n... B. mm. m z 1 a m- 8.... he... 4 Y I I. I 1 n 13 5 0205 0 91 00001 2 u 12 5 22 0 1 6 an am 7 m 607 50004 H n 4 10 1 3 9 w .3 mwwmfi 5 2 .0 .1 38075 2 .1 5 77 19 5 1% 7 365 n w. 1 1 1 2 1 L3. u 4 0205 5 50 00001 e e e 26 00 5. amaa a 3 mm 3...? 8 .2 m MN MW mmm 5 0 00 L4 3 5 1 1 3 0 3 11 5 5 1 0 I 2 1 1 S .90 2 5 M 3 3 mmmme a 02.05 0 a mmwmm 7 mm m m m m mm "MW 2 0 m 7%1 4 220 L 99 685 W. n 3 2 1 3 6 1 1 1. 1 3 0 N 2 4. O2 5 5 00 08 6 00 0 0 9 756 0008 5 14.85 52 0 09 91 5m5 2 0205 0 55 00002 1 1 BN0 m 11 m 3 10 1 3 5 22 0 L &a mnm 2 1s 5 0 Y H u 1 13' 0 3 5 000 0 no 734 50007 59 0 5 I: 40 00 03 F H 2 a n .1 mm% 822 1 L La %mm 435 5 u y 1 m 3 1 n 1... 1 9,65 s m ammmm t $22.0 0 8 0 545 4 000 n C "M u 2 2 5 5 4.5 1 4 1 3 u u .m fimmmfi "L 665 m 1 1 BN0 9 r y I 3 8 .0 I 1 1 1 D n n I H E W 000 S .09 1 0205 191 00 9 3 0 5 2 058 0007 S 5 5 L u K0L2 3mmm5 m 2 L 0 7 nan H Mwmv I .m m :l B n m w 3 110 3 13 A T A n B R N 707 u u n n u n T u A 2 0 0 n 4 04m WNNWWW S 5.7.8 u T 822 L 8m 7 985 N w mm u n m n a 10 2 7 containing the compound of this invention have improved processing safety as indicated by the improved Mooney scorch time and faster curing rates as indicated by the Rheometer data; and that these improvements are achieved without substantially changing the properties of the vulcanizates.

Table III demonstrates the activity of other compounds of the invention and Table IV demonstrates the applicability of the invention in synthetic rubber compositions.

Although the invention has been illustrated by typical examples, it is not limited thereto. Changes and modifications of the examples of the invention herein chosen for purposes of disclosure can be made which do not constitute departure from the spirit and scope of the invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A compound of the formula 8 wherein X is hydrogen, lower alkyl, lower alkoxy, nitro, chloro, bromo, iodo or hydroxy and n is one or two; when n is one R is alkyl of 1-20 carbon atoms, cycloalkyl of 5-12 carbon atoms, aralkyl of 7-10 carbon atoms or aryl of 6-12 carbon atoms; when n is two R is alkylene of 1-8 carbon atoms.

2. A compound of claim 1 wherein X is hydrogen. 3. A compound of claim 2 wherein R is phenyl.

4. A compound of claim 2 wherein R is cyclohexyl. 5. A compound of claim 2 wherein R is isopropyl. 6. A-compound of claim 2 wherein R is cyclooctyl.

7 References I s J UNITED STATES PATENTS 3,645,98'i 2/1972 Kerwood 26o .3os 3,689,467 9/1972 Boustany et a1. 260305 *RICHARD GALLAGHER, Primary Examiner 

